1. Field of Invention
The present invention relates generally to a low thread force two piece cable tie with an improved locking structure. More particularly, a strap accepting channel is provided with a protruding support guide and the locking device is sized to be capable of filly piercing the strap so that a free end of the locking device is supported on the protruding support guide, which provides increased resistance to removal while achieving a lower insertion force.
2. Description of Related Art
Plastic cable ties having metal locking device inserts are well known in the art. Examples of such include U.S. Pat. No. 3,457,598 to Mariani and U.S. Pat. No. 5,517,727 to Bernard et al.
Cable ties of this type include a metal locking device partially embedded at an angle within a strap accepting channel of a cable tie head. The metal locking device is situated at an angle that allows insertion of a cable tie strap in an insertion direction, but allows for engagement of the locking device with the strap when it is pulled in a removing direction to prevent removal. The metal locking device of such conventional cable ties is in the form of a cantilevered beam that is fixed at one end and extends into the strap accepting channel at the free end.
It has always been a desirable feature to have a cable tie that is easy to use while maintaining its locking strength. To increase locking force, one option has been to increase the thickness of the locking device. However, this has been found to have an adverse affect on the insertion force necessary to install the cable tie, which is undesirable. The converse is also true, attempts to reduce insertion force have resulted in use of thinner metal locking devices, which while reducing insertion force have the undesirable affect of reducing the locking force of the cable tie.
Thus, there is a need for an improved locking device that can provide better resistance to removal while achieving a low insertion force.
There also is a need for an improved cable tie that has more flexibility of the cable tie strap, particularly near the locking head.
It is therefore an object of the invention to provide a cable tie utilizing a metal locking device that has improved retention strength and a low insertion force.
It is another object of the invention to provide a two piece cable tie with a locking device that converts from a cantilever beam to a simple beam support when fully engaged to increase resistance to cable tie removal.
It is another object of the invention to provide a two piece cable tie that has increased flexibility of the strap near the locking head without necessarily reducing or compromising strength of the cable tie.
The above and other objects are achieved by a cable tie comprising a strap including a first end and a free end, a locking head having a strap accepting channel, and a metal locking device mounted within an anchoring region of the head to form a cantilever beam having a mounted end fixed to an end wall of the locking head and a free end positioned within the strap accepting channel. The strap includes a central inwardly projecting groove of a predefined width that defines a thinned portion extending along a longitudinal axis of the strap to the free end of the strap. The strap accepting channel has a channel width W1 defined between an end wall and the inner wall. The strap accepting channel also includes a support guide projecting from the inner wall of the locking head into the strap accepting channel to restrict the width of the channel accepting channel to a width W2, which is less than W1. The free end of the metal locking device has a length L that is greater than W2. The support guide has a width transverse to the width of the strap accepting channel that is less than the predefined width of the projecting groove of the strap. The support guide also includes a ledge that provides a support surface for the metal locking device that changes the locking device from one having a cantilever support to one with a simple beam support when the locking device is bent downward by a sufficient withdrawal force. This withdrawal force is sufficient to cause the locking device to fully pierce the thinned portion of the strap, which allows the free end of the locking device to rest upon the ledge.
The invention also provides a method of bundling an object by: placing the cable tie around an object; inserting the free end of the strap into the strap entry end of the strap accepting channel and beyond the free end of the metal locking device; and feeding the free end of the strap through the strap accepting channel until the cable tie is snug around the object. The cable tie can be locked by applying a removal force to the cable tie acting to pull the strap out of the strap entry end of the strap accepting channel that causes deflection of the free end of the metal locking device toward the strap entry end of the strap accepting channel so as to fully pierce the strap and rest the free end of the metal locking device against the ledge of the support guide.
The invention also achieves increased cable tie strap flexibility by forming an end of the strap adjacent the locking head with a groove of increased width to provided a thinned portion that allows greater freedom of movement.